Short for Extensible Markup Language, a specification
developed by the W3C. XML is a pared-down version of SGML, designed
especially for Web documents. It allows designers to create their own
customized tags, enabling the definition, transmission, validation, and
interpretation of data between applications and between organizations.

"This tutorial provides a brief overview of XML to help you become
familiar with the markup language's most common features. After reading
the tutorial, you should be able to read examples that use XML syntax
and understand the basic structure of an XML document. The tutorial
concentrates on the technical rather than the business side of XML, and
is aimed at technical specialists such as software engineers and
documentation writers who are approaching XML for the first time."